Basal Metabolic Rate (Harris-Benedict)

What This BMR Calculator Does and Who It's For

This tool estimates your basal metabolic rate (BMR): the number of calories your body burns at complete rest to keep essential functions running, such as breathing, circulating blood, and regulating temperature. It uses the revised Harris-Benedict equations, one of the most widely used methods for estimating resting metabolism.

BMR is useful for anyone planning their nutrition: people trying to lose weight, gain muscle, or simply maintain their current weight. Because it represents the calories you burn before any movement, it forms the baseline you build a daily calorie target on top of.

How the Harris-Benedict Formula Works

The calculator uses the 1984 revised Harris-Benedict equations, which differ by sex. Weight (w) is in kilograms, height (h) in centimeters, and age (a) in years:

• Men: BMR = 88.362 + (13.397 x w) + (4.799 x h) - (5.677 x a)
• Women: BMR = 447.593 + (9.247 x w) + (3.098 x h) - (4.330 x a)

Reading the Equation

Each term reflects how a factor changes metabolism. Weight and height carry positive coefficients, so larger bodies burn more calories at rest. Age has a negative coefficient because resting metabolism tends to decline as you get older. The constant at the start (88.362 for men, 447.593 for women) anchors the result.

If you measure in pounds and inches, convert first: divide pounds by 2.205 to get kilograms, and multiply inches by 2.54 to get centimeters.

Worked Example

Take a 30-year-old man who weighs 80 kg and is 180 cm tall. Plugging into the male equation:

BMR = 88.362 + (13.397 x 80) + (4.799 x 180) - (5.677 x 30) = 88.362 + 1071.76 + 863.82 - 170.31 = 1853.6 calories per day.

This means his body burns roughly 1,854 calories daily even if he stayed in bed all day. To find total daily calories, multiply BMR by an activity factor: about 1.2 for sedentary, 1.55 for moderate exercise, or 1.725 for very active. At 1.55, his maintenance need is around 2,873 calories.

Tips, Common Mistakes, and Factors That Affect Your Result

BMR is an estimate, not a precise measurement. The Harris-Benedict equation does not account for body composition, so two people of the same weight can have different real metabolisms if one carries more muscle. Muscle burns more calories at rest than fat, so very lean or very muscular people may find the formula slightly under- or over-estimates their needs.

• Don't confuse BMR with total daily energy expenditure; BMR excludes all activity, so always apply an activity factor for real-world calorie targets.
• Use current measurements and update them as your weight changes, since the result shifts with every kilogram.
• Check your units; entering height in inches or weight in pounds without converting will produce a wildly wrong number.
• If you're very muscular or have low body fat, the Katch-McArdle formula (which uses lean body mass) may estimate your BMR more accurately.